1. Field of the Invention
The present invention relates to a coating apparatus for applying at a predetermined spacing to a surface of an object a liquid such as a synthetic resin or a paint. The present invention relates also to a coating apparatus wherein it has a slit shaped die which is subjected to cleaning each time when the coating operation is interrupted. Furthermore, the present invention relates to a coating device for applying, to an article having a first surface already applied with a liquid, a liquid at the opposite second surface at locations which are aligned with the locations where the liquid is applied at the first surface. The present invention can be suitable for applying a liquid synthetic resin to an aluminum or copper foil which is used for producing a re-chargeable battery such as a lithium ion type.
2. Description of Related Art
Known in a prior art is a coating apparatus for applying, at a predetermined spacing, a liquid such as a liquid synthetic or a paint on an object to be applied, such an endless sheet of a synthetic resin or paper or foil, or lengths of sheets of glass or wafer, which device is provided with a conveyor for obtaining a horizontal movement of the object to be applied with the liquid and a slit die located above the conveyor and formed with a liquid injection nozzle. The coating device is further provided with a drive mechanism such as a fluid cylinder for generating a movement of the slit die vertically or horizontally with respect to an object on the conveyor in such a manner that the liquid injection nozzle is moved between a liquid applying position (operating position) and a rest position.
This type of the coating device is defective in that, during an application process of the liquid, some of the applied liquid, in the shape of droplets, is likely to be attached to a tip end of the liquid injection nozzle. The droplets are, together with the liquid from the nozzle, applied to the surface of the object, which makes it difficult to obtain an uniformly applied layer of the liquid.
To overcome this difficulty, Japanese Unexamined Patent Publication 7-80386 discloses a cleaner for removing the droplets of the liquid attached to a tip end of the liquid infection nozzle. Namely, this cleaner is provided with a cleaning mechanism arranged at an end of the conveyor. When a cleaning of the liquid injector is necessary, the slit die is, first, raised from the operating position, by a predetermined amount, to a rest position and is, then, moved horizontally toward the cleaner.
The above-mentioned construction for making the slit die to be moved vertically or horizontally is disadvantageous in that the movement of the slit die must be slow in order to prevent a large impact force from being generated when the slit die is stopped.
Furthermore, in the prior art wherein the vertical and horizontal movements of the slit die are repeated, the impact forces as generated upon the stoppage causes variations to be generated in a vertical spacing between the liquid injecting position of the slit die for executing the application operation as well as in a horizontal position of the slit die with respect to the object, thereby generating unevenness in the thickness of the applied layer of the liquid as well as a deviation of the liquid applying position from the desired position.
Furthermore, the prior art is also disadvantageous in that the cleaning operation of the liquid nozzle of the slit die requires a mechanism which allows the slit die to be moved in both the vertical and horizontal directions, which makes the mechanism to be complicated, on one hand, and, on the other hand, makes the stoppage time, for executing the cleaning operation, long and which reduces the production efficiency.
The coating apparatus is used also for applying liquid on both surfaces of a resin film. In this case, an application of liquid is, first, done on the first surface (front surface) of the film, so that spaced applied layers are formed on the first surface. Then, an application of the liquid is done on the opposite surface (rear surface). The timing of the application of the liquid to the rear surface is controlled so that the applied layers of the liquid on the rear surface are in a registered condition with the opposite layers of liquid is on the front surface. In order to do this, a sensor is provided at a location upstream from the slit die for detecting a position of a length of applied liquid on the front surface of the film. A calculation of the timing for starting and stopping of the application of the liquid (for rotating the liquid feed pump) is done based on the rotating speed of an electric motor for feeding the film, i.e., the speed of the movement of the film. The operation of the feed pump at the calculated timings cause a length of the liquid to be formed on the rear surface of the film.
This register control is however defective in that a slippage of the film fed by a roller mechanism as well as an elongation of the film, which are inevitable, cause errors to be generated in the positions for the commencement and or the interruption of the application of the liquid and, thereby, liquid layers to be misregistered between the front and rear surfaces, which causes the product quality to drop.